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rawtopgm - convert raw grayscale bytes into a portable graymap
rawtopgm
[-bpp [1|2]] [-littleendian] [-maxval N] [-headerskip N] [-rowskip N] [-tb|-topbottom]
[width height] [imagefile]
Reads raw grayscale values as input.
Produces a PGM file as output. The input file is just a sequence of pure
binary numbers, either one or two bytes each, either bigendian or littleendian,
representing gray values. They may be arranged either top to bottom, left
to right or bottom to top, left to right. There may be arbitrary header
information at the start of the file (to which rawtopgm pays no attention
at all other than the header's size).
Arguments to rawtopgm tell how to
interpret the pixels (a function that is served by a header in a regular
graphics format).
The width and height parameters tell the dimensions
of the image. If you omit these parameters, rawtopgm assumes it is a quadratic
image and bases the dimensions on the size of the input stream. If this
size is not a perfect square, rawtopgm fails.
When you don't specify width
and height, rawtopgm reads the entire input stream into storage at once,
which may take a lot of storage. Otherwise, rawtopgm ordinarily stores
only one row at a time.
If you don't specify imagefile, or specify -, the
input is from Standard Input.
The PGM output is to Standard Output.
- -maxval
N
- N is the maxval for the gray values in the input, and is also the maxval
of the PGM output image. The default is the maximum value that can be represented
in the number of bytes used for each sample (i.e. 255 or 65535).
- -bpp [1|2]
- tells the number of bytes that represent each sample in the input. If the
value is 2, The most significant byte is first in the stream.
The default
is 1 byte per sample.
- -littleendian
- says that the bytes of each input sample
are ordered with the least significant byte first. Without this option,
rawtopgm assumes MSB first. This obviously has no effect when there is
only one byte per sample.
- -headerskip N
- rawtopgm skips over N bytes at
the beginning of the stream and reads the image immediately after. The default
is 0.
This is useful when the input is actually some graphics format that
has a descriptive header followed by an ordinary raster, and you don't have
a program that understands the header or you want to ignore the header.
- -rowskip N
- If there is padding at the ends of the rows, you can skip it
with this option. Note that rowskip need not be an integer. Amazingly,
I once had an image with 0.376 bytes of padding per row. This turned out
to be due to a file-transfer problem, but I was still able to read the image.
Skipping a fractional byte per row means skipping one byte per multiple
rows.
- -bt -bottomfirst
- By default, rawtopgm assumes the pixels in the input
go top to bottom, left to right. If you specify -bt or -bottomfirst, rawtopgm
assumes the pixels go bottom to top, left to right. The Molecular Dynamics
and Leica confocal format, for example, use the latter arrangement.
If
you don't specify -bt when you should or vice versa, the resulting image
is upside down, which you can correct with pnmflip .
This option causes
rawtopgm to read the entire input stream into storage at once, which may
take a lot of storage. Ordinarly, rawtopgm stores only one row at a time.
For backwards compatibility, rawtopgm also accepts -tb and -topbottom
to mean exactly the same thing. The reasons these are named backwards is
that the original author thought of it as specifying that the wrong results
of assuming the data is top to bottom should be corrected by flipping
the result top for bottom. Today, we think of it as simply specifying the
format of the input data so that there are no wrong results.
pgm(5)
,
rawtoppm(1)
, pnmflip(1)
Copyright (C) 1989 by Jef Poskanzer.
Modified June 1993 by Oliver Trepte, oliver@fysik4.kth.se
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